Substantial evidences implicate that sample preparation and protein extraction in proteomic studies of plant-pathogen interactions are critical to understand cross talk between host and pathogen. Therefore, interest is growing in applying proteomics techniques to investigate simultaneously secreted proteins from rice and pathogen. We have found, however, that most proteins of interest are low abundant so that proper prefractionation or extraction of secreted proteins from extracellular space (ECS) in the rice leaf is required to excavate relevant protein. This chapter describes the preparation of sample and extraction procedure to enrich the proteins interested before separation by 2-DE or LC-MS/MS. This method significantly increases the sensitivity of proteomic comparisons.